The mechanisms underlying stimulation of B cells to replicate and to differentiate into immunoglobulin secreting cells will be studied in three populations of cells: a) splenocytes from adult mice; b) splenocytes from neonatal mice; and c) murine B leukemia cells. The role of surface immunoglobulin and receptors for T cell factors will be dissected by using monoclonal antibodies against microns or delta purified interlukins to stimulate such cells. We will attempt to determine the role of surface IgM and IgD both in signaling for proliferation and differentiation e.g., is the activating signal given by surface immunoglobulin similar in each instance. Efforts will be made to stimulate IgM secreting cells to switch to IgG secretion in order to define the stimuli for isotype switches as well as to elucidate underlying molecular mechanisms. Ia antigens on T cells from selected peritoneal exudate lymphocytes in the guinea pig will be studied at the primary structural level both by comparative peptide mapping and by terminal amino acid sequencing. T cell recognition of virus infected cells will be analyzed further with particular emphasis on the role of the carbohydrate moeities of H-2D and H-2K and of viral glycoproteins. This will be pursued in the liposome model using tunicamycin treatment of cells to yield surface proteins that are not glycosylated. Amino acid sequencing studies will be performed on thymus leukemia antigens and Qa-2 antigens in order to determine their relationship to other MHC gene products. Abelson virus will be used to transform B cells and to determine which subpopulation of the cells are susceptible to transformation and to determine changes in surface molecules of the transformed cells.